The present invention relates to an image forming device such as a copying machine, a scanner, a printer, and a versatile all-in-one machine having various features of them.
As has already been disclosed in a prior art document like Japanese Unexamined Patent Publication 2000-61027, an electrical device and a communication terminal device, which are characterized by an energy saving feature, are usually provided with two power sources, namely, a primary power source used during a normal mode operation and a, secondary power source used during an energy saving mode operation. The latter energy saving power source supplies electric power to functional units, such as an operation unit and a call signal detection unit, which require a certain minimum amount of power during standby.
Configured with two power sources as mentioned above, however, those devices still consume an amount of power that is not negligible. For instance, in the aforementioned devices, functional units therein are supplied with power all at once from the primary power source when the current operation mode is switched from energy saving mode to normal mode. This means that some standby units that are currently not used are supplied with power.